This invention relates to an induction system for an engine and more particularly to an improved engine induction system that permits the attainment of good performance throughout the entire engine speed and load range.
As is well known, many factors in the design of an internal combustion engine affect their performance. Also, the design of certain factors to achieve optimum performance at one speed and/or load range may deteriorate performance at other speed and load ranges. A typical example of this is the design of the induction system. In order to provide maximum power output, the induction system should provide good charging efficiency which necessitates the absence of turbulence in the intake charge. However, if no turbulence is generated in the induction system and combustion chamber under low speed low load conditions, poor combustion and performance can result. There have, therefore, been proposed systems for cooperation with the induction system to generate turbulence under only certain running conditions. Examples of such induction systems may be found in the copending applications of Yoshiharu Isaka, entitled "Tumble Control Valve for Intake Port," Ser. No. 834,604, filed Feb. 12, 1992 and "Intake Air Control System," Ser. No. 839,111, filed Jun. 3, 1992, which applications are assigned to the assignee hereof.
In the arrangement shown in those patents, there is provided a control valve in the induction passage which is generally positioned at a point adjacent where the induction passage communicates with the valve seat of the cylinder head and at an area where the intake passage has a generally angularly related shape with the control valve positioned at the bight. Although this arrangement is extremely effective in providing the desired degrees and types of turbulence in the combustion chamber under low and mid range performance and no turbulence at high speeds, the flow control pattern which can be accomplished with this type of control valve has some restrictions.
In addition to the question of generating turbulence in the combustion chamber, it is also the practice to tune the length and effective cross-sectional area of the intake passage so as to achieve maximum volumetric efficiency. However, an induction system that is tuned to achieve maximum volumetric efficiency and power at the high speed will be relatively inefficient for charging at low speeds and low load conditions. Although arrangements have been incorporated for changing the tuning of an individual intake passage, this has been done conventionally by changing the effective length of the passage. However, such length changing devices add to the bulk of the induction system with obvious disadvantages.
Specifically, it may be desirable to provide an arrangement wherein the actual shape of the intake passage may be reconfigured so as to change the direction in which the flow passes through the valve seat and also to tune the intake passage for different speed and load conditions.
It is, therefore, a principal object of this invention to provide an improved intake system for an internal combustion engine wherein the actual configuration of the intake passages may be changed during engine running.
It is a further object of this invention to provide an improved induction system for an internal combustion engine wherein the intake port configuration and the flow pattern generated by it can be changed during engine operation.
If it is desired to provide a change in the actual configuration of the induction passage as opposed to providing a flow directing device in the induction passage as in the aforenoted co-pending applications, then this must be done in such a way that facilitates making the change while not unduly complicating the cylinder head.
It is, therefore, a still further principal object of this invention to provide an improved induction system for an internal combustion engine wherein the configuration of the intake passages may be changed during engine operation while maintaining a relatively simple and easily operated structure.